Expand 6 x 2TB with 6 x 3TB = 16.6TB ? (raid z2)

[Brosif_My_Nif]

Guys,

I have a stupid question that I can't seem to find the answer for.

I had an initial Vdev of 6 x 2TB HDD's (Raid-Z2). This was getting me 7.2TB of space after formatting (going off my memory). I was running out of space, so I used the GUI to expand the Zpool with a second Vdev of 6 x 3TB HDD's (Raid-Z2). It recognized the 3TB HDD's just fine.

After adding the 2nd Vdev to the first, my total usable space for this Zpool is 16.6TB. From my calculations after formatting, I should be getting 18TB's of space.

Is this just me messing up on my calculations and the total usable space should be 16.6TB or am I truly missing 1.4TB's of space after formatting?


Thank you in advance for your time!

 

[Brosif_My_Nif]

Well, I think I found my own problem after searching all day. I had a few snapshots that were taking up a lot of space. I deleted ALL the snapshots and now have a total of 17.8 available. It is still a little lower than the 18.2 that I calculated here: http://www.servethehome.com/raid-calculator/

However, this is much more do-able.